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Room-Temperature, Inflated Balloon                   Is that Kirsten's icy stare deflating the balloon? Or is it...Liquid Nitrogen???

No, that can's not being crushed by the strength of Laura's grip...it's the Ideal Gas Law!!

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Day 3: Balloon H-R Diagram. We supplied the students with sturdy foam board, big party balloons, smaller water balloons, markers, and tape. We instructed them to create their own H-R diagram, using the appropriate sizes and colors of balloons.

Tips:
1) Water balloons are REALLY hard to blow up. I wouldn't use those next time.
2) The students sort of had a tendency to copy their diagrams from figures in their notes. I would consider not letting them use their notes, in order to force them to think things through. Still debating on that one.

The sweat of Jared's lungs (Open Cluster Group)                       Team Globular Cluster's HR Diagram

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Observing:
Globular cluster people observed M5 (for a pretty picture) and M13 (for a pretty pic and a CMD). The open cluster group observed M11 and NGC 6819. They observed two clusters to observe what changes in data between clusters of significantly different ages.

We observed in B,V,R. We intended to use only B and V images for our CMDs-- R is needed for three-color images. CMDs made with B and V seem to work just fine.

"Long" exposures tended to be between 70 and 120 seconds, as hinted at by the

Late-Night Open Cluster Party

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3-Color Images:
Pretty 3-color images are really easy to make, as long as you have decent images in B, V, and R (or any three filters!) We suggest using DS9-- it's really simple and intuitive, and has the added bonus that DS9 is the tool astronomers actually use!

We just downloaded the newest version of DS9 and made an RGB image in under 5 minutes. You can too! Easy step by step directions:

1) Calculate shifts between your three images. Shifts greater than 1 pixel or so will be evident in your images, and we don't want that. We had our students measure the shifts. They picked the same five stars or so in each band (one in each corner, and one in the center) and measured the centroid of each using IRAF imexam ('r' command). Then, they calculated the shift from band to band for each star. Finally, they averaged all the shifts for the stars, and used this as their final shift.

2) Now, if DS9 behaved itself and didn't try to be too smart, you could just apply the shifts you've found using IRAF imshift. However, as Kirsten learned the hard way, imshift neglects to put some crucial information in the shifted image's header, so when you display it with DS9, the image is not shifted at all. So, what we would suggest is, shift your image with a simple program in IDL which removes the header. Of use imshift, but then delete the header. Be creative! But test your method before showing it to the students.

3) See if you have the newest version of DS9, on your relevant computer. The easiest way to do this is start up DS9 like usual, click on "Frame" up at the top, and see if directly under "New Frame" it lists "New Frame RGB". If it does, skip to step 4. If it doesn't, then you need to download the newest version.

4)

True-Color M11, in BVR                                                                   NGC 6819 in BVR

True-Color M13, in BVR                                                                   M5 in BVR

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Data Reduction:
We decided to have our students brave the jungles of daophot. We used the stand-along version of Daophot for Mac OSX. We got this software from Mike Bolte-- he might give it to you, too, if you take his class or ask nicely. The trickiest parts of this software were a) finding enough Macs to run it on (we had to borrow our friends' powerbooks) and b) a 'daomaster' which has mysteriously stopped working on Macs (we had to run this last step on a Linux machine).

Software you need installed on you Mac for this plan: DS9 or Ximtool, IRAF, and the daophot stand-alone software. You will also need our macro script, which automatically runs all the daophot scripts and does lots of tedious iterations. It was originally developed by Katy Flint, and was improved by Jenny Graves. It can be downloaded

M11 Color Magnitude Diagram--Click for a larger image             NGC 6819 CMD

M13 Color Magnitude Diagram

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Isochrone Fitting:
We used

M11 CMD with 0.2 Gyr isochrone overlain                                 NGC 6819 CMD with 3 Gyr isochrone

M13 CMD with 19 Gyr isochrone

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Calculating Distances:
Now that our students had found good isochrone fits to their clusters, they "knew" the cluster absolute magnitudes from the isochrone models. So all we had to do to get distances was callibrate our apparent magnitudes.

We've thought of two ways to callibrate the data, and we're not sure we have much faith in either. The first is a rather pitiful excuse for a "method"-- we look up published CMDs of our clusters, and shift our observations' instrumental magnitudes to fit the published apparent magnitude values. The second way is more scientific, and actually appeared to work ok this year: we actually use standard stars and run daophot on them to get their brightnesses. The shift between the stars' "standard" value and "our" value should be the same as the shift between our clusters' instrumental value and their true apparent value. I think.

***We all know callibration is never as easy as it sounds. For goodness sake, see if it works and makes sense before trying to callibrate in front of your students!!!***

We didn't do anything fancy like worry about reddening terms, or even about dust. We used the very simplest distance modulus equation:
m - M = 5 log d - 5 with d in parsecs.

So, to recap, "M" comes from the isochrone models. "m" comes from your newly callibrated data. We shifted our isochrone transparency around to match up with our CMD, and then looked at the difference between the two y-axes. That's "m-M"! Our students did a bit of algebra (they knew logarithms pretty well) to extract the only unknown, "d".

Our results didn't match the best with published values-- especially for M13. Use sub-solar isochrones for globs!!! Also, um, think about your calibration more than we did. If you wanted to be really hard-core, you could teach your students (and yourself) about errors. Below are our measurements.

M11: 2600 pc

NGC 6819: 1400 pc

M13: 1000-3000 pc

As our students so astutely observed, But wait! I thought NGC 6819 was supposed to be farther away than M11! And M13 the farthest of all! Our distances need help.

We tended to use the published distances for our galaxy models.

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3-D Galaxy Models, to Scale:
Now that we know the distances to our star clusters, we can put them in the grander context of the Milky Way Galaxy. Kirsten and Laura went to the Art Supply shop, the Lumber yard, and to their own closets to find the following supplies:
-- Large pieces of black foam board (for the galactic disk)
-- Assorted sizes of styrofoam balls (~8" diameter for a big galactic bulge. ~1" for a star cluster)
-- Red felt (to cover styrofoam balls for galactic bulges)
-- Pom Poms (multi-color)
-- X-acto Knives
-- Glue Gun
-- Lots of Glitter Glue (to make stars!)
-- Milky Pen (writes on Black board-- so students can label the Sun, etc.)
-- Dowels (two for each galaxy, each a bit longer than the disk's diameter)
-- Wire (for attaching the dowels together, and for hanging the galaxy and clusters from the dowels)
-- Wire cutters

We first talked about galactic features and scales. What is a bulge? How big is it? How far away from it are we? How long is it from one end of the galaxy to the other? etc. We also talked about galactic coordinates, and had our students look up the galactic coordinates for our clusters.

Some of our students chose to use the entire piece of foam board (~3' x 3') to make their galactic disks. However, we noticed that there was no "to-scale" styrofoam bulge for a disk this size. So some of our students chose to be sticklers about scale, and make smaller disks with to-scale bulges.

Our students cut their styrofoam bulges in half with kitchen or X-acto knives. Then they covered them in the felt, and glued it on with the glue gun. They attached one half of the bulge to the center of foam board, and the other half to the underside of the foam board.

Our students decorated their disks with the glitter glue and Milky Pen. They labelled the Sun's location and drew in spiral arms.

Next, it was time to hang the galaxies. For each model, we took two dowels, and held them at right angles to each other, in their centers, to make a cross. We tightly wrapped wire around their intersection, to hold them together. Then we cut four pieces of wire, and our students made four holes evenly spaced in the outskirts of their disk. Each wire attached a corner of their disk to a dowel. So the galaxies hung! We usually needed two people for this process. We also found that the galaxies could be better observed if they were hung at some inclination. Finally, tie another piece of wire around the dowel intersection, so that the galaxy can hang from the ceiling.

Finally, our students made four star clusters out of styrofoam balls or pom poms: two open clusters, and two globular clusters. They attached these clusters in their correct places around the galaxy, given their galactic coordinates and distances. For clusters which were far from the galactic plane, we attached the clusters to (stiff) wire, and had them sticking up above the plane. I suppose that if the cluster was very high above the plane, it could dangle from the dowels. The students labelled the clusters.

We really enjoyed this project, and we think our students did too. We had each student make their own model, which is nice, but not necessary. The supplies can be a bit expensive. We'd probably allot 3-4 hours for this project, next time we did it.

Here are some photos of our students' lovely Milky Ways:

Catherine, Amanda, and Kirsten with their Galaxies           Molly and Becca with their Milky Ways (Jared not pictured here)

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Our Students' Brilliant Presentations:
Our students worked really hard on their presentations, which they presented to their cluster-mates and the Robotics/Nanotech Cluster. Download their powerpoint files below:

Open Clusters in the Spotlight

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Some General Conclusions:
We really liked having NGC 6819 there as an intermediate-age representative.

The Open Cluster group was able to deal with both M11 and NGC 6819. In the future, Open and Globular clusters could conceivably be combined into one project. But that would mean no intermediate-age cluster, probably.

Kirsten, any final words of advice? Do you wanna mention submitting M5 to APOD?

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